1. Field
The disclosed aspects relate to wireless communication networks, and more particularly, to systems, methods and apparatus for providing wireless communication devices' robust slotted mode operation in fading wireless environments.
2. Background
Wireless communication devices, such as cellular telephones, portable computers and the like, have rapidly gained in popularity over the past decade. These devices are increasingly becoming multifaceted devices capable of providing a wide-range of functions. For example, today's cellular telephone may also embody computing capabilities, Internet access, electronic mail, text messaging, GPS mapping, digital photographic capability, an audio/MP3 player, video gaming capabilities, video broadcast reception capabilities and the like.
The multifaceted nature of wireless communication devices results in the devices being used more frequently and, thus, more power is consumed. Wireless communication devices are conventionally powered by a battery. The longer the battery stays charged, the longer the user is able to utilize the wireless communication device without having to connect it to a recharger or otherwise replace the battery. While technological strides are being made to increase the power afforded to wireless device batteries and conserve the use of battery power so as to increase the performance time of the device, the need continues to exist to make further improvements in this area.
When a wireless communication device is switched on but not actively engaged in communicating user data, it typically operates in an idle mode. However, the term “idle mode” is somewhat of a misnomer because while the wireless communication device resides in the idle mode, the device performs various tasks that enable it to be ready for use, either to initiate or receive a call. Specifically, while in the idle mode the wireless communication device is constantly turning components and applications on and off; on to perform vital functions and off again to conserve battery power.
The tasks that the wireless communication must perform while in idle mode are often specified by the standards within which the wireless communication is to operate. These mandatory tasks are rather power consuming because they involve the radio receiver.
Included within the mandatory tasks is the ability of the wireless communication device to wake periodically and turn on its radio receiver briefly to see if it has been paged, which means to find out if there is an incoming call (mobile termination call) or a message. This periodic waking occurs on what is known as a slot cycle of a slotted mode. The purpose of the slot cycle is to permit the phone to keep the receiver turned off most of the time as a means of conserving battery life. When the wireless communication device first registers with a base station, the base station and device determine which paging channel the device will use (if there is more than one) and what phase of the slot cycle that mobile will use. Thereafter, the phone wakes periodically, turns its receiver on briefly to see if it has an incoming call or if there is other traffic from the cell it must respond to, and if there is nothing then it shuts the receiver down again and waits until the next slot time.
When an incoming call arrives at a base station for a given wireless communication device, the phone system of the caller generates the sound of a phone ringing as a comfort tone back to the caller, and the base station waits until the slot time for the called wireless communication device. When the slot occurs, the cell sends a message to the wireless communication device telling it that there is an incoming call. This causes the device to waken and set up the call, and to begin to ring. If the device doesn't respond to the page, the cell may try again on the next slot. The advantage of a longer slot cycle is that the device spends a lower percentage of the time with its receiver on and thus the battery will last longer. It also means there is more capacity on the paging channel. The advantage of a shorter slot cycle is that the device gets more chances to receive the page, and will receive the page sooner.
When the wireless communication device operates in the slotted mode, the device first, upon entering a slotted mode wake-up, attempts to acquire the active set pilot of the current system or cell that it is in communication with before it can decode the paging channel. If the wireless communication device fails to acquire the active set pilot during the slot, the device declares the system as being lost and enters into the system determination state, otherwise referred to as the system acquisition state. The system determination state provides for re-acquiring the system that has been lost or acquiring another system/cell. However, as appreciated by those skilled in the art, re-acquiring or acquiring a system is power intensive operation that requires the receiver to remain operative for an extended period of time to tune to the proper frequency and such.
Field studies have shown that when a wireless communication system is lost by the wireless communication device, in a high percentage of instances the device will re-acquire the same system back that was lost within a relatively short period of time. This is generally believed to be due to the wireless communication device determining a short fade, in which the signal strength deteriorates (i.e., fades) below an acceptable level for a short period of time before it strengthens to an acceptable level. Thus, if the wireless device is configured to re-acquire the system each time the device encounters a short fade during a slot wake-up, unnecessary battery power is consumed.
Therefore a need exists to improve the robustness of slotted mode operation to improve wireless communication device power consumption and, thus, improve standby time performance. In particular a need exists to improve slotted mode operation performance in instances in which the wireless communication device is determining fading or otherwise spotty coverage conditions.